1. Field of the Invention
This invention generally relates to a method for brazing tungsten carbide particles and diamond crystals in one operation, and more specifically relates to a method for brazing tungsten carbide particles and diamond crystal in one operation to a metal substrate to produce an improved abrasive tool.
2. Prior Art
Abrasive tools typically comprise a hard abrasive particle, such as diamond crystals or tungsten carbide particles, adhered to a substrate, such as a metal substrate. For example, abrasive tools comprising tungsten carbide particles brazed to a metal substrate and abrasive tools comprising diamond crystals brazed to a metal substrate are known in the art. Thus, prior techniques predominantly have involved either independently brazing tungsten carbide particles to a substrate or independently brazing diamond crystals to a substrate. Due to production and material costs of diamond tooling, tungsten carbide has been commonly used as an economical replacement when cutting or grinding requirements would allow.
Prior art methods of brazing diamond crystals to metal substrates have required the use of vacuum or reducing atmosphere furnaces operating at 1300.degree. C. or less. The primary brazing alloy for brazing diamond crystals to metal substrates comprises a cobalt or nickel base and contains a certain percentage of chromium.
Prior art methods of brazing tungsten carbide to metal substrates utilize similar procedures and equipment to the methods for brazing diamond crystals to metal substrates. However, there is a wider range of braze alloys which are suitable for wetting to the tungsten carbide particles than there are for wetting to the diamond crystals. These braze alloys include the cobalt, nickel, and copper based alloy families. Prior attempts at utilizing copper as a braze alloy in diamond brazing has had limited success due to the lack of the ability of the copper to wet to the diamond crystal. This would produce little or no adhesion of the particle to the substrate.
U.S. Pat. No. 4,018,576 to Lowder et al. discloses a diamond abrasive tool and method of manufacture. The Lowder patent teaches a direct brazing technique of diamond crystals to a substrate surface using a brazing alloy of the cobalt and/or nickel base type which contains certain percentages of chromium. The Lowder method is characterized in that it teaches that by using a specific composition for the brazing alloy, no pre-conditioning of the diamond surface is necessary to obtain the wetting of the diamond surface by the brazing alloy. The brazing alloy used in the Lowder method comprises from 60 percent to 90 percent nickel or cobalt or mixtures thereof, up to 12 percent boron, silicon and/or phophorous, and 2 percent to 30 percent chromium.
U.S. Pat. No. 4,039,700 to Sohmer et al. discloses a hard metal coating process for metal objects. In the Sohmer patent, hard metal granules containing tungsten carbide are deposited onto a steel saw blade with a binder material comprising nickel alloys, cobalt alloys or low-melting iron alloys with boron and/or silicon. The steel blade then is heated in a protective gas atmosphere using a high-frequency electric current which provides an induction loop to cause the brazing. The preferred binder material comprises 84 percent nickel, 10 percent cobalt and no copper or chromium.
U.S. Pat. No. 4,749,594 to Malikowski et al. discloses a method for coating surfaces with hard substances. The Malikowski process utilizes a silver-based brazing alloy comprising 60 percent to 90 percent silver, 2 percent to 35 percent copper, 2 percent to 30 percent tin and/or indium, and 2 percent to 20 percent of certain other metals. Silver-based brazing alloys typically are less economical than copper-based and/or nickel-based alloys. Further, silver-based brazing alloys do not have the range of applicability as do copper-based alloys and nickel-based alloys.
Diamond crystals have exceptional durability and long lasting characteristics when used in the abrasive setting. Tungsten carbide particles have the ability to develop extremely sharp cutting edges and make exceptional abrasive tools. Typically, while the methods for brazing diamond crystals and tungsten carbide particles independently to substrates are similar, the brazing alloys most suitable for each are not the same. Therefore, it can be seen that there is a need for a method for brazing combinations of diamond crystals and tungsten carbide particles to metal substrates utilizing a single, economical brazing alloy.